# std::ranges::views::empty, std::ranges::empty_view

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< cpp‎ | ranges

Defined in header `<ranges>` |  |
template<class T> requires std::is_object_v<T> class empty_view : public ranges::view_interface<empty_view<T>> | (1) | (since C++20)
namespace views { template<class T> constexpr empty_view<T> empty{}; } | (2) | (since C++20)

1) A range factory that produces a `view` of no elements of a particular type.
2) Variable template for `empty_view`.

### Member functions

begin [static] | returns nullptr (public static member function)
end [static] | returns nullptr (public static member function)
data [static] | returns nullptr (public static member function)
size [static] | returns ​0​ (public static member function)
empty [static] | returns true (public static member function)
##### Inherited from std::ranges::view_interface
cbegin (C++23) | returns a constant iterator to the beginning of the range. (public member function of `std::ranges::view_interface<D>`)
cend (C++23) | returns a sentinel for the constant iterator of the range. (public member function of `std::ranges::view_interface<D>`)
operator bool | returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of `std::ranges::view_interface<D>`)
front | returns the first element in the derived view. Provided if it satisfies `forward_range`. (public member function of `std::ranges::view_interface<D>`)
back | returns the last element in the derived view. Provided if it satisfies `bidirectional_range` and `common_range`. (public member function of `std::ranges::view_interface<D>`)
operator[] | returns the `n`th element in the derived view. Provided if it satisfies `random_access_range`. (public member function of `std::ranges::view_interface<D>`)

## std::ranges::empty_view::begin

static constexpr T* begin() noexcept { return nullptr; } |  | (since C++20)

`empty_view` does not reference any element.

## std::ranges::empty_view::end

static constexpr T* end() noexcept { return nullptr; } |  | (since C++20)

`empty_view` does not reference any element.

## std::ranges::empty_view::data

static constexpr T* data() noexcept { return nullptr; } |  | (since C++20)

`empty_view` does not reference any element.

## std::ranges::empty_view::size

static constexpr std::size_t size() noexcept { return 0; } |  | (since C++20)

`empty_view` is always empty.

## std::ranges::empty_view::empty

static constexpr bool empty() noexcept { return true; } |  | (since C++20)

`empty_view` is always empty.

### Helper templates

template<class T> constexpr bool ranges::enable_borrowed_range<ranges::empty_view<T>> = true; |  | (since C++20)

This specialization of ranges::enable_borrowed_range makes `empty_view` satisfy `borrowed_range`.

### Notes

Although `empty_view` obtains `front`, `back`, and operator[] member functions from `view_interface`, calls to them always result in undefined behavior since an `empty_view` is always empty.

The inherited operator bool conversion function always returns false.

### Example

Run this code

    #include <ranges>

    int main()
    {
        namespace ranges = std::ranges;

        ranges::empty_view<long> e;
        static_assert(ranges::empty(e)); // uses operator bool
        static_assert(0 == e.size());
        static_assert(nullptr == e.data());
        static_assert(nullptr == e.begin());
        static_assert(nullptr == e.end());
        static_assert(nullptr == e.cbegin());
        static_assert(nullptr == e.cend());
    }

### See also

optional (C++17) | a wrapper that may or may not hold an object (class template)
ranges::single_viewviews::single (C++20) | a `view` that contains a single element of a specified value (class template) (customization point object)
views::all_tviews::all (C++20) | a `view` that includes all elements of a `range` (alias template) (range adaptor object)
ranges::ref_view (C++20) | a `view` of the elements of some other `range` (class template)

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